Donald Ford, a retired engineer in London, says all the European Union has done is make everything feel “terribly different” – and not in a good way.

One thousand miles away, at the other edge of the EU, Michal Nielub, a local activist in Poland, says the bloc that Poles so clamored to join has lost its allure. “We have to cooperate with the West, but [Western leaders] have to think about our goals, our identity, our national interests,” he says, sipping tea at a cafe in Slupsk. “I have got a lot of friends, and when we are talking about the European Union, they say they want to exit.”

Sybille Hamann, a journalist at an outdoor cafe in Vienna, says she can barely believe these conversations. After living through “20 years of pro-European euphoria,” she is astonished at how much the mentality of many Europeans has changed from a sense of tighter unity to one of disintegration. Sahd Jaballah, coordinator of a youth center in Mechelen, Belgium, puts it more simply. “It feels like we’re going back 60 years,” he says.

Melanie Stetson Freeman/Staff

Donald Ford, a retired engineer in London, says that with all the immigration he often feels like a foreigner in his own country.

Across the Continent, the basic question – what is Europe? – is being asked in living rooms, corporate suites, and government cubicles with more urgency than at any time since World War II.

Buffeted by fundamental changes – the decision by Britain to leave the EU, the continuing torrent of refugees, the inexorable rise of far-right political parties, and the threat posed by a resurgent Russia – the EU is confronting a historic crisis of cohesion and identity.

Many experts fully expect the EU to survive. They believe this is simply the latest in a recurring cycle of challenges. Others think the EU will be a weakened and much less unified bloc of nations in the future – and possibly a much smaller one as well.

While comparisons of the current period are made with the run-up to World War II, when a depression made Europe ripe for fascism, or with ​the disruptive globalization that preceded ​World War I​, many dismiss the notion that Europe is about to face anything as cataclysmic. But there is no doubt that Europe finds itself at a hinge moment – one that will have significant implications for the world’s largest trading bloc as well as for the Western world and the kind of democracy it espouses.

“The ​... certainties of political and economic order have been overturned,” says Brigid Laffan, director of the Robert Schuman Center for Advanced Studies at the European University Institute in Florence, Italy. “And of course [this is] all against the background of the rise of other [countries, such as China], but also extraordinary technological change. Societies are entering what some people call a period of liquid modernity ... it’s hard to get ahold of.”

Ms. Laffan says publicly standing in defense of the EU is not something that she usually does, viewing herself as a scholar of, not an advocate of, the EU. But that’s exactly what she did when she penned an opinion piece in the Irish Times titled “In defense of the European Union” days after the “Brexit” vote.

“It is time for those people in our societies that want to live in a rule-bound, tolerant, open, liberal way – I think we’ve got to stand up and be counted,” she says. “I think it’s important not to let the fruits of the post-Second World War order disappear.”

Bulgarian Government/AP/File

Then British Prime Minister David Cameron (below, r.) and Bulgarian Prime Minister Boyko Borisov (c.) talk in December 2015 in front of a fence built along the Bulgarian-Turkish border to control the flow of migrants.

Alexander Carius certainly understands all the implications of the changes sweeping across Europe. He is a low-key man on a high-minded mission: trying almost single-handedly to get Germans to confront the future of European society.

Mr. Carius, a German policy adviser who on this day is wearing a crisp white button-down shirt and jeans, is helping to stage a series of town hall meetings across the country encouraging people to wrestle with some of the most important questions behind the Continent’s identity crisis: How safe do Gemans feel? What about Chancellor Angela Merkel playing the role of Welcome Wagon lady of Europe? Will the far-right reshape German politics?

Mr. Carius conceived of the “Open Society” debates last fall over dinner with a friend as asylum-seekers were pouring into Germany. At the time, France was still rocked by a marauding terrorist attack. Right-wing political parties were gaining followers across Europe.

Today those criticizing the basic tenets of the EU still have plenty of momentum. They are creeping up in polls in many countries and dominating airwaves, siphoning voters away from the establishment political parties that have governed Europe with a consensus toward closer ties and more tolerance since the end of World War II.

Melanie Stetson Freeman/Staff

'I always thought that we were taking one step after the other towards more [European] integration. And all of a sudden...you see...it's not going to happen.' – Sybille Hamann, a journalist in Austria

This fall, for instance, Austrian voters could very well elect the EU’s first far-right head of state. Yet the shift rightward isn't monolithic. In a surprise move, Hungary on Oct. 2 failed to pass a referendum that would have closed its doors to refugees. More than 98 percent of voters did support the initiative, but not enough turned out at the polls – fewer than the threshold limit of 50 percent – to officially pass the referendum. It was a rebuke to Hungarian prime minister Viktor Orbán, a leader of the anti-immigrant movement in Europe.

For Carius, the debating salons are aimed at countering the prevailing narrative that says the EU and all it stands for are irredeemably evil. The group has 50 talks planned now and hopes to stage another 365 events between now and German national elections next fall. “I see no alternative,” he says from his sleek office in a trendy neighborhood of Berlin overlooking the Spree River.

While German residents debate the philosophical underpinnings of Europe, bureaucrats in Brussels are working out the details of something that will hold far more practical implications for the future of Europe – Britain’s pending divorce from the EU. The EU just held its first summit in Bratislava, Slovakia, on Sept. 16 to discuss where the bloc is going from here, without the British leader, new Prime Minister Theresa May.

In their vote to leave the EU in June, most who were in favor of leaving weren’t motivated by the desire to dismantle Europe. Instead they were driven by a heady mix of defiance and pride over issues of identity and sovereignty and frustration over their own economic plight. They were men like Mike Phillips, an accountant in the heart of Leicestershire in central England, the birthplace of fox hunting, who scoffed at those predicting Britain’s demise after it leaves the world’s largest single market. “Who is not going to trade with us?” Or Mike Crone, a retired carpenter puffing on a pipe on a bench nearby in Market Harborough, who oozed optimism. “We were a stand-alone country before. Why can’t we do it now?”

Melanie Stetson Freeman/Staff

'I have been in France since 1984...but if you are African and you say you are French, they always say, but from where?' – Galaye Gueye, a tailor in Paris from Senegal

Britain, of course, has always been a hesitant European partner. It joined the bloc only in 1973, after its empire was largely a footnote in history and its economy was reeling from deindustrialization. Under leaders from Winston Churchill to Margaret Thatcher, Britain has always had a fraught relationship with continental Europe.

But the decision to definitively leave the EU surprised even the “Leave” campaign – prompting a sense of “buyer’s remorse” among some Brexit supporters and sending a jolt of support for the EU across the Continent. Various opinion surveys from Denmark to Finland showed desire for similar referendums plummeting after Brexit.

Still, the risk of copycat exit movements remains, especially if populists gain ground in countries where euroskepticism is highest, such as France. And Brexit could change Europe’s architecture in other ways. Pro-European Scots now want to try again to break free from a Britain sitting outside the EU. If Scottish secessionists were to vote and win, they’d buoy other separatist movements, such as in Catalonia in Spain.

Europe, in the meantime, has been shaken out of complacency, given a glimpse into the consequences of not responding to the issues Europeans care most about. That includes fortifying exterior borders to make Europe more secure, bringing order to the refugee crisis, generating jobs (especially for European youth), and rethinking assumptions that Europeans actually want “more Europe.”

In some ways, Brexit has acted as an accelerator. “When you formulate [what the EU will look like without Britain] what you are really doing is formulating your own ideas about the future of Europe,” says Jan Techau, a foreign-policy expert at the American Academy in Berlin. “They are all positioning themselves for the kind of EU they want afterwards.... We are in the middle of the discussion of what the EU needs to look like four or five years from now.”

But that Europe looks very different from the way it did a decade ago, in the years of EU expansion. That was a moment of optimism, as post-Soviet states joined the bloc and the assumption was that the EU was a project of linear, often liberally minded, progression with no turning back. Until now.

Asel Llana

'I feel European, but actually I don't know how to define it. What does it mean "European"?' –Veronika Bonebakker of Banska Bystrica, Slovakia

The town of Ostrý Grúπ in the Banská Bystrica region of central Slovakia looks unremarkable on the surface. But its outsize history includes a day of infamy. The descendants of victims of World War II call it “Bloody Sunday.” On Jan. 21, 1945, Nazi soldiers, retaliating against partisans and their supporters living throughout its hills, burned down Ostrý Grún and shot 64 villagers, women and children among them, dead.

Yet when the nation went to the polls to choose new leadership in Slovakia’s national elections in March, nearly a fifth of this town voted for the extreme right People’s Party Our Slovakia (L’SNS), which openly praises the Nazi puppet state installed during the war.

“From my position, I can’t understand why residents choose this way to show their frustration about their current discontent,” says Jana Angletova, the mayor of Ostrý Grún, whose father survived the massacre as a baby only because he was hidden under a duvet.

The discontent here is part of a larger wave of populism from France to the Netherlands to Germany. But it is the movement’s foothold in the post-Soviet states that perhaps worries Brussels the most. These are the states, after all, that yearned to join the EU in the 1990s, both for the funds they would receive and for the security protection the association provides, especially against Russia.

Poland, once the poster child of postcommunist Europe, elected into office last year the ultraconservative Law & Justice party, which is clashing with Europe over whether Warsaw is backsliding on democracy.

Sara Miller Llana/The Christian Science Monitor

‘I support the European Union, but only it if it good for us.' – Maria Milagros, a Spanish Civil War survivor from Spain

Hungarian Prime Minister Viktor Orbán, who has cozied up to Russian President Vladimir Putin, has faced the same charges. Slovakia, which holds the rotating EU presidency right now, sued the EU over its policy to relocate refugees across the bloc.

Observers in the post-Soviet states explain the growing euroskepticism as a product of the passage of time, especially for the countries’ youth. First-time voters were key to the L’SNS success at the polls in Slovakia. “They were not personally involved in the fight [against communism],” says Grigorij Mesežnikov, head of the Bratislava-based Institute for Public Affairs. “They take democracy for granted.”

No one understands this sentiment better than Stanislav Mičev. Soft-spoken but driven by a mission, Mr. Mičev is the director of the Museum of the Slovak National Uprising in Banská Bystrica. As his title implies, he travels across the region to talk to youths about their history and what extreme right, anti-EU politics really portend for Slovakia. Now he feels a new urgency in his job. “They are not aware of how fragile our politics are,” he says.

Melanie Stetson Freeman/Staff

'I feel European inside of me...but Europe sometimes makes mistakes. Because some of them feel strong, and have power, they use it for bad, not for good.' –Alexandros Apostolopoulos, a pensioner in Greece

As populism has grown across the West, many fault mainstream politicians for failing to respond – for either just pandering to the populist vote or for failing to convince Europeans to believe in the EU decades after peace has held. “The postwar elites across Europe have not really solved any major problems in 30 years,” says Mr. Techau of the American Academy. He calls it “sophisticated state failure.”

No major reform is expected until Germany and France hold elections next year. But then tough questions will hang over the bloc. Techau says he believes it’s not refugees or Brexit that threatens to drive the EU apart, but a half-developed currency system. He says eventually politicians will have to integrate the economic system further – which he admits no one wants – or possibly watch other countries leave the eurozone, or even see it fail altogether.

The question of unity lies at the heart of the problems facing mainstream politicians in Europe, who have to balance national interest against the greater good of the EU project. Solidarity is needed at every policy turn, from where to house refugees to how to respond to Russia’s incursion in Ukraine. Since the Greek debt crisis, the unity has all but vanished.

Melanie Stetson Freeman/Staff

Migrants from Pakistan and Bangladesh sit together in April in the Moira camp on the Greek island of Lesbos. They are protesting the government’s deportation of migrants to Turkey. To them, the Moira camp had become more like a prison than a migrant holding center.

These tensions and clashes of interest are starkly visible on the northern Greek island of Lesbos, and specifically from a seat at To Kyma (The Wave), a low-key beachfront restaurant and hotel that looks out onto the Aegean Sea. Paris Laoumis, whose family has owned this restaurant for decades, says that the eurocrisis has threatened his financial well-being – as it does the rest of debt-stricken southern Europe.

Last summer, when financial controls were imposed on Greeks after populist leader Alexis Tsipras rejected Brussels’s latest austerity demands and the country faced bankruptcy, people started canceling reservations at Mr. Laoumis’s restaurant at the height of the tourist season. And yet his restaurant quickly filled up – not with flush customers but with the rush of refugees that started crossing through Europe.

Less than 10 miles from Turkey, his restaurant and hotel sit across from a beach now strewn with discarded life jackets. Ever since other European nations shut their borders to refugees, the migrants have been stuck in Greece, many at a processing center in Lesbos – a situation that has scared off even more tourists.

“Last summer, we were the ones actually blamed for not following the rules,” says Kostas Bakoyannis, governor of the central region of Greece, referring to the country’s opposition to the EU’s austerity rules. “We were the ‘bad boys’ of Europe. Now suddenly we are the ‘good boys and girls of Europe’ [for helping the migrants]. We have been following the rules, and we are asking others to do the same.”

Melanie Stetson Freeman/Staff

'[Last summer] we were the "bad boys" of Europe. Now suddenly we are the "good boys and girls" [for helping the migrants.]' – Paris Laoumis (c.), a hotel and restaurant owner on the Greek island of Lesbos

European solidarity has broken down the most, in fact, over the question of migration, specifically Muslim migration. In Poland, for instance, the governor of the conservative state of Podkarpackie, in the southeastern part of the country, asked local mayors in 2015 if they would host refugees. Not a single one offered.

Jerzy Paul, a former mayor and national parliamentarian, is unapologetic about his rejection of Muslim refugees in Polish society. Nor does he see any hypocrisy in his stance. “People here are not against the [migrants’] religion but against terrorism,” he says. “Poles who emigrate usually have jobs, help to build economies, and they integrate with local societies. They don’t terrorize others.”

Few Muslims reside in this part of Europe, but such messages are heard across the Continent – and are threatening to drive communities even further apart. After successive terrorist attacks by Islamist-inspired perpetrators – in France, Belgium, and this summer in Germany for the first time – Muslims have said that they feel pushed away. This could become one of Europe’s biggest problems, as alienation breeds radicalization.

After the bombings in Brussels, for example, Anass El Lamzi, a son of Moroccan immigrants from the picturesque Belgian town of Mechelen, says his identity was suddenly in flux. All it takes is an angry stare by passersby on the street or metro, he says, to undo years of integration. “In those moments, I don’t feel Belgian. I don’t necessarily feel Moroccan either – I feel in between,” he says. “It’s strange. I have always been a good guy. I’m always polite to people. But when the attacks happened, everyone – the public, the media, even my colleagues – generalized about Muslims.”

He says after the bombings, his cousin, who works in a Brussels public school, told him that some of the Muslim students actually hailed the attacks. “They said, ‘We hate Belgians.’ ”

European leaders are struggling to find the right balance between safety and openness. Many residents feel insecure, and while most don’t conflate terrorism and religion or immigration, refugees and asylum-seekers have played a role in the terror hitting Europe. Bans on burqas – and burkinis at beaches in France – epitomize the public debate playing out. All of it pushes Muslims farther away.

For Mechelen’s mayor, Bart Somers, it is the identity of the town, whose magnificent center is dominated by the 14th-century St. Rumbold’s Cathedral, that has to expand to absorb newcomers. At the end of the day, his goal is simple: “that the identity of our city is not based on the past, but on the future.”

Jacky Naegelen/Reuters/File

The Eiffel Tower is lit in blue, white, and red, the colors of the French flag, to pay tribute to the victims of a series of terror attacks in November 2015.

Germany’s Angela Merkel, whose leadership is crucial to the future of Europe, has appealed to calmer heads with a similar message. She has traveled around the Continent trying to rally cooperation on the EU’s toughest issues before Brexit negotiations begin.

At home, though, she faces rising opposition. Last month, her center-right party lost elections to the populist Alternative for Germany in her home district in northeastern Germany. “Change isn’t a bad thing,” she told lawmakers just days after the vote, acknowledging the uncertainties of the era. “Germany will remain Germany, with everything we hold dear. I’m very convinced that if we keep our composure and stand by the truth, then we’ll win – and we’ll win back the most important thing we need, the trust of the people.”

German author Andre Wilkens would probably agree. He believes Germany is central to Europe’s future. “This is not the time to sit back on your designer Italian sofa and watch some dancing show or read some cookery books,” says Mr. Wilkens, who has a book coming out on where Europe is going.

“My take is, we have created a really wonderful thing with the EU. It is probably one of the best things Europeans have managed to create,” he says. “In that context, we must say, ‘OK, there are problems. Let’s work them out....’ ”